Food Source Information Sweet Corn

Sweet corn (Zea mays var. rugosa) comes in three colors: yellow, white, and bicolored. Sweet corn contains a genetic mutation on the su locus that causes the endosperm to store at least twice as much sugar as field corn. As soon as corn is harvested, the sugar begins converting to starch, reducing the sweetness. Therefore, sweet corn should be refrigerated or preserved within two to six hours of harvest to ensure best quality and retention of sweetness.

There are hundreds of different varieties, including Bodacious, Incredible, Temptation, Delectable, and Providence. Traditional varieties of corn are su1 (sugary1) mutants and contain twice the sugar and eight to ten times more water-soluble polysaccharide as field corn. The increase in water-soluble polysaccharide results in a creamy consistency but is also responsible for corn’s short shelf life (maximum storage in refrigerator of four days). Supersweet varieties that contain the sh2 (shrunken2) mutation contain at least four times the amount of sugar as field corn but almost no water-soluble polysaccharide, making conversion of sugar to starch almost negligible. This allows Supersweet varieties to remain sweet up to 14 days after harvest if kept refrigerated, making these varieties ideal for sale at distant markets.

Top producers in the U.S. include Washington, Minnesota, Wisconsin, California, Oregon, and Florida. Sweet corn grown in the Midwest is generally available late summer through early fall while sweet corn grown in Florida is available December through May.

While there have not been many foodborne outbreaks related to sweet corn, there have been foodborne outbreaks related to frozen vegetables in which corn was included. Between 2000 and 2020, at least 39 corn-associated outbreaks were reported to CDC’s National Outbreak Reporting System (NORS), causing 1,859 illnesses, 99 hospitalizations, and 2 deaths.

In 2013, a multistate outbreak of Listeria monocytogenes was reported with a total of nine illnesses and three deaths. Epidemiological and laboratory evidence indicated that frozen vegetables from a frozen foods company in Washington State were the source. In late spring of 2016, there was a large recall of frozen vegetables with corn being one of the implicated vegetables. After the recall no further linked cases were reported. In June of 2018, a multi-country outbreak of Listeria monocytogenes was discovered in frozen corn and other vegetables from a Hungarian company. This outbreak affected Austria, Denmark, Finland, Sweden, and the United Kingdom. The Hungarian Food Chain Safety Office ordered a recall of products and stopped all freezing activity in June, 2018. Genetic sequencing led to the discovery that frozen corn and other frozen vegetables tested positive for Listeria monocytogenes. There were 47 confirmed cases of Listeriosis and 9 deaths.

In addition to these outbreaks, frozen corn has been the subject of recalls due to potential contamination with Listeria monocytogenes. In 2017, Giant Food Stores, Martin’s Food Markets and Stop & Shop Supermarkets each voluntarily recalled their store brand frozen whole sweet corn due to potential contamination from a shared supplier. The name of the supplier was not publicly identified. No reported cases of listeriosis were reported in association with this recall.

Pre-Harvest

Seeds of sweet corn should be planted about one inch deep in heavy soils and two inches deep in sandy soils. It is highly recommended that all seeds are treated with insecticide and fungicide, which can sometimes be applied before purchasing seed and should be verified with the supplier. If Supersweet seeds are used, they must be planted about a half an inch shallower than other sweet corn seeds, and planting should be delayed until warmer temperatures in the soil are reached. The corn earworm is the greatest insect concern with sweet corn. Commercial sweet corn operations require the use of an insecticide spraying program to manage this pest.

One sweet corn plant should be placed every nine to 12 inches. Three-foot rows with this spacing will allow for about 17,000 plants per acre of cropland. Fertilizer can be applied depending on the soil type. To obtain a desirable appearance, a high level of nitrogen must be maintained in the soil. Moisture is crucial for sweet corn growth. It will contribute to crop uniformity, early enhancement, increased yields, and other desirable qualities. However, over-irrigation of sweet corn cropland can cause seeds to easily rot, especially in cold weather. Thus, irrigation must be closely monitored, and seeds should be planted during the warm season. Diseases are rare with sweet corn.

Harvest

The average yield per 100 feet of row is about eight dozen ears of corn. Sweet corn is ready for harvest at approximately 15 to 23 days after the silks appear. If the weather is especially hot, the plant will tend to mature faster. When the kernels are fully developed, they are in the milk stage and will leak a milky liquid when punctured. Sweet corn can be harvested by hand or machine. A large commercial operation will likely use machines for harvest. It is important that the ears be collected in the early morning or evening when the weather is cool.

Post-Harvest

It is extremely important to keep the corn cool following harvest. Sweet corn loses sweetness and freshness very quickly after harvest, especially when kept at increased temperatures. Because sweet corn has a high respiration rate, it produces heat which can build up in bulk loads after harvest. The longer it takes for the corn to be chilled and the longer it is able to stay at elevated temperatures, the more sugar is able to be converted to starch, thus greatly affecting quality of the product. Product must be moved quickly from the field to the packing shed where it should be sorted, packed, and cooled. There are several methods to chill sweet corn: hydrocooling using water, package icing (typically only used for local distribution), and cold storage using refrigeration and a relative humidity of at least 90-98%. It is ideal to store corn at 32 °F.  No matter how the corn is transported to market, it must be kept on ice to maintain quality.

Because of the conversion of sugar to starch, fresh sweet corn should be refrigerated or processed immediately after harvest. From a food quality perspective, sweet corn should be consumed within four to ten days after refrigeration, depending on the varietal. Fresh-cut sweet corn kernels are extremely perishable, with very high respiration rates, making proper temperature control critical.

It is not uncommon for fresh corn to be preserved via canning. However, improper home-canning practices can leave low-acid foods, such as corn, at risk of developing C. botulinum. Corn cannot be safely canned using a boiling water bath; it must be processed in a pressure canner. Home-canned corn should be heated to no less than 80 degrees Celsius for at least 10 minutes. Before consuming canned corn products, containers should be inspected for bulging, lid damage, and leakage, as these are signs of gas release produced by bacterial growth.

There have been no reported outbreaks of food-borne illness associated with sweet corn, however, there have been foodborne outbreaks related to frozen vegetables in which corn was included. While there are concerns regarding various mycotoxins in field corn fed to animals, there is minimal risk associated with mycotoxins in sweet corn consumed by humans. According to the FDA, minimal traces of, fumonisins (a type of mycotoxin), have been found in sweet corn (4-82 ppb).This is 50 to 1,000 less than the maximum recommended levels in corn intended for human consumption (4 ppm). Additionally, according to the FDA, aflatoxin, another mycotoxin of concern in field corn, has been found in corn from southeastern states. However, aflatoxin may be found in corn grown in other regions depending on growth practices, harvesting practices and storage conditions.

Corn is one of the most versatile food products grown and consumed in the United States. In addition to fresh sweet corn for human consumption, it can be further processed into other food products, sweeteners, starches, oils, alcohol, and ethanol-based fuel. Corn is also the main feed grain in the United States and is projected to account for around 95% of the feed grain in 2015–2016. As of 2010, Americans were consuming an average of 26 pounds of sweet corn per person. Of this total amount, 9.6 pounds were from frozen sweet corn, 9.1 pounds were fresh sweet corn, the remaining 7.4 pounds were canned sweet corn products. In the 2006–2007 Foodnet Population Atlas of Exposures, 41.5% of the survey cohort reported eating fresh corn within the past seven days.

For information on how to keep corn fresh and of safe quality please visit FoodKeeper App.

While sweet corn typically invokes images of summer barbeques, it also has many health benefits. Sweet corn is a great source of Vitamin C and Vitamin A, with one ear of corn containing over 10% of the Daily Value (DV) of Vitamin C and over 6% DV of Vitamin A. One large ear of boiled corn on the cob contains 113 calories, 4 grams of protein, 1.8 grams of fat, 5.4 grams of sugar, and 2.8 grams of fiber (10% DV). The large amount of soluble fiber helps decrease cholesterol. Research has shown that cooking corn actually increases levels of beneficial antioxidants and phytochemicals.

1. Brecht JK. The Commercial Storage of Fruits, Vegetables, and Florist and Nursey Stocks Agriculture Handbook Number 66: Sweet Corn [Internet]. United States Department of Agriculture Agricultural Research Service; 2016 [cited 2020 Feb 26].
2. Centers for Disease Control and Prevention. Foodborne Disease Active Surveillance Network (FoodNet) Population Survey Atlas of Exposures, 2006-2007 [Internet]. Centers for Diseases Control and Prevention (CDC): U.S. Department of Health & Human Services; 2006 2007 p. 16–26. (FoodNet Population Survey Atlas of Exposures).
3. Centers for Disease Control and Prevention. Multistate Outbreak of Listeriosis Linked to Frozen Vegetables (Final Update) [Internet]. 2016.
4. Dewanto V, Wu X, Liu RH. Processed Sweet Corn Has Higher Antioxidant Activity. J Agric Food Chem [Internet]. 2002 Aug 1 [cited 2015 Feb 22];50(17):4959–64.
5. Food and Drug Administration. Compliance Program Guidance Manual: Chapter 03 Foodborne Biological Hazards [Internet]. [cited 2020 Mar 17].
6. Giant, Martin’s, Stop & Shop recall frozen corn for Listeria risk [Internet]. Food Safety News. 2017 [cited 2021 Jul 27].
7. Haynes C, Everhart E, Jauron R. Sweet Corn [Internet]. Iowa State University, Horticulture Guide, Home Gardening. 2002.
8. Iowa State Extension. Food of the week: Sweet corn [Internet]. [cited 2015 Feb 13].
9. Nolte K. Sweet Corn [Internet]. Yuma County Cooperative Extension. [cited 2020 Mar 17].
10. Nutrition C for FS and A. Background Paper in Support of Fumonisin Levels in Corn and Corn Products Intended for Human Consumption [Internet]. [cited 2015 Feb 22].
11. Penn State Extension. Sweet Corn — Home Food Preservation [Internet]. Home Food Preservation (Penn State Extension). [cited 2015 Feb 22].
12. Planting Sweet Corn in the Home Garden | Horticulture and Home Pest News [Internet]. [cited 2020 Mar 17].
13. Postharvest Cooling and Handling of Sweet Corn | NC State Extension Publications [Internet]. [cited 2020 Mar 17].
14. Rapid risk assessment: Multi-country outbreak of Listeria monocytogenes serogroup IVb, multi-locus sequence type 6, infections linked to frozen corn and possibly to other frozen vegetables – first update [Internet]. European Centre for Disease Prevention and Control. 2018 [cited 2020 Feb 25].
15. Schneider K, Silverberg R, Chang A, Goodrich Schneider R. Preventing Foodborne Illness: Clostridium botulinum [Internet]. University of Florida IFAS Extension. 2015. Available from: https://col.st/qtE9M
16. Sweet Corn [Internet]. [cited 2020 Mar 17].
17. Sweet Corn | University of Maryland Extension [Internet]. [cited 2020 Mar 17].
18. Sweet Corn Production [Internet]. Penn State Extension. [cited 2020 Mar 17].
19. U.S. Department of Agriculture Foreign Agricultural Service. Global Agricultural Trade System | Sweet corn, 2014 [Internet]. [cited 2015 Feb 22].
20. U.S. Department of Agriculture. Basic report 11168, corn, sweet, yellow, cooked, boiled, drained, without salt [Internet]. [cited 2015 Feb 22].
21. U.S. Department of Agriculture. Vegetables Annual Summary, 2019 [Internet]. [cited 2020 Feb 25].
22. USDA Economic Research Service. Corn – Background [Internet]. United States Department of Agriculture Economic Research Service. 2015.
23. USDA Economic Research Service. U.S. Sweet Corn Statistics [Internet]. USDA Economics, Statistics, and Market Information System. 2010.
24. Giant, Martin’s, Stop & Shop recall frozen corn for Listeria risk [Internet]. Food Safety News. 2017 [cited 2021 Jul 27].